Non-explosive rock breaking is well established. A cartridge containing a charge of combustible material is inserted into a drilled hole in the rock, the hole is sealed using sand (a process called “stemming” in the industry) and the charge ignited. A high volume of a harmless gas is produced which has the effect of splitting the rock.
The same technique is used for breaking up man-made concrete structures and the term “rock breaking” as used herein is to be construed as including the breaking of both naturally occurring rock and man-made structures with rock-like characteristics.
One commercially available cartridge is known as the “NONEX” cartridge. Nonex cartridges are supplied in a wide range of sizes (both in length, in diameter and in charge size) and substantial numbers must be purchased and held in stock to ensure that all rock breaking situations that arise can be dealt with.
It is possible to use a number of Nonex cartridges simultaneously by suitably wiring them to the firing circuit. However, a practical difficulty is that the cartridges ignite in sequence and the first cartridges to ignite can sever the wires to the cartridges which are to fire later, with the result that some cartridges do not fire. This means that difficulties are encountered in clearing the broken rock as it has live cartridges buried in it.
A further commercially available system is known as the “Boulder Buster”. This can only be used in a vertically drilled hole. A number of cartridges are dropped into the hole and the hole is then water filled. The uppermost cartridge is ignited and the downward pressure on the cartridges below ignites them in sequence. Each cartridge includes a pressure activated cap.
U.S. Pat. Nos. 4,900,092 and 5,670,737 describe such cartridges.
The present invention provides a rock breaking system which has advantages over the two known systems described above.